The invention relates to a medical instrument for electrosurgery.
Such an instrument is used, for example, for performing endoscopically assisted interventions in the human or animal body in the context of minimally invasive surgery.
With an electrosurgical medical instrument of the present invention, biological tissue can be sectioned and/or coagulated under the effect of high-frequency current. Two jaw parts, of which at least one is movable, are usually arranged at the distal end of the tubular shaft, the present invention being especially advantageous in those medical instruments in which both jaw parts are movable. Depending on the intended surgical purpose of such an instrument, the jaw parts are designed as cutting tools with cutting edges, in order to sever tissue in the body, or they are designed as gripping tools with surfaces striking bluntly against one another in order to grip severed tissue with the jaw parts and remove it from the body, or in order to hold an organ or a vessel with the aim of keeping it away from the operating site. The jaw parts can also have a combination of a cutting function and a gripping function.
If the instrument has two jaw parts, at least one of the two jaw parts is connected to the tubular shaft in an articulated manner, while the other jaw part is connected to the tubular shaft either rigidly or, once again, in an articulated manner.
In a medical instrument of the type mentioned at the outset, it is further provided that at least one jaw part has an electrode that can be acted upon with high-frequency current. If the instrument is designed as a bipolar electrosurgical instrument, as is also preferred in the context of the present invention, both jaw parts each have an electrode that can be acted upon with high-frequency current, said electrodes having different polarities. Both electrodes of the two jaw parts can accordingly be connected, separate from one another, to a respective pole of a high-frequency voltage source. By acting on the electrodes of the two jaw parts, the cutting action, in the case of a design as a cutting tool, can be increased by the thermal action of the high-frequency current in the tissue, and, on the other hand, in the case of a design as a gripping tool, tissue gripped between the jaw parts can be coagulated by the heat build-up, and bleeding of the tissue can thus be stopped.
In electrosurgical medical instruments of this type, the current supply to the at least one electrode of the at least one movable jaw part generally causes problems. In bipolar instruments in particular, the two jaw parts have to be adequately electrically insulated from one another in the area of the hinge forming the pivot axis of the at least one jaw part. An electrical separation of the two jaw parts in the area of the hinge is necessary, especially in bipolar instruments, because the electrodes of the two jaw parts are connected to different potentials. The problem of the electrical separation of the two jaw parts from one another is greater, the smaller the design of such an instrument in the area of the jaw parts and thus in the area of the hinge. However, a narrow design of the instrument in the area of the jaw parts is particularly important for minimally invasive surgery.
In an instrument known from document WO-A-00/36986, the distal end has two jaw parts, of which only one is movable, both jaw parts each having a metallic main body, which main bodies are connected to one another in an articulated manner in the area of the pivot axis. On their sides facing each other, the metallic main bodies each have an insulator element, the respective electrode of the respective jaw part being applied to these insulator elements so that the electrodes are electrically separated from the metallic main body. A current supply line runs to each of the two electrodes via the hinge, said current supply lines being designed as wire-shaped elements and being insulated from one another. In this configuration of the jaw parts, it is possible for the jaw parts in the area of the hinge to be made of metal and thus be particularly stable.
A disadvantage of this configuration is the nature of the current supply to the respective electrode in the form of the rectilinearly extending, wire-shaped element. Upon opening and closing of the jaw parts, that is to say when the at least one movable jaw part is moved, the wire-shaped element is permanently bent and stretched again. These constant changes of load occurring over the lifetime of the instrument lead relatively quickly to a fatigue fracture of the wire-shaped element in the area of the pivot axis, as a result of which the instrument does not provide a long service period, that is to say the lifetime of this instrument is undesirably shortened.
To eliminate this problem, a sliding contact has therefore been provided, for the at least one movable jaw part, which taps the current at the hinge forming the pivot axis of the at least one movable jaw part, the current supply line ending accordingly at the hinge. The provision of a sliding contact in the area of the hinge is, however, very complex in terms of construction and is very difficult to achieve, especially in very small instruments.
The document WO-A-01/15614 discloses an electrosurgical medical instrument, in particular a bipolar medical instrument, having two jaw parts, of which one is movable. In the area of their articulated connection, the two jaw parts have a main body made of an electrically insulating material, on which is secured an electrically conductive jaw part insert forming the associated electrode. The current supply to the electrode of the movable jaw part is effected via the axially movable force transmission element provided for opening and closing the jaw parts, while the electrode of the non-movable jaw part via a rectilinear, wire-shaped element which is connected proximally to the tubular shaft likewise serving as current supply and whose distal end is connected to the electrode of the non-movable jaw part.
If the second jaw part were also to be made movable, this would entail the same problem as in the known instrument described above, namely that the wire-shaped element would be permanently subjected to bending and stretching stresses, which in the long run would again lead to fracturing of the wire-shaped element.